Glass to metal seal and parts thereof and method of making same



May 11, w c

GLASS T0 METAL SEAL A AND METHOD OF Filed ADIll ND PARTS THEREOF MAKING SAME 30, 1948 X m v F -fwe am zm x m y 1 r W Iatented May 11, 1954 UNITED STATES ATENT OFFICE SAME Irvin W. Cox, West Alli Hammer, Ina, Milw of Delaware Application April 30, 1948,

s, Wis., assignor to Cutleraukee, Wis., a corporation Serial No. 24,128

4 Claims. (01. 29-1795) This invention relates to glass to metal seals and parts thereof and methods of making the same. The invention relates more particularly to metal members of suitable form composed of integrally united layers or laminations of different alloys of metals, one of said alloys being adapted to provide a perfectly tight and unusually strong seal with high melting point glasses and another of said alloys being adapted to substantially match the non-linear thermal expansion characteristics of such glasses.

A primary object of the invention is to provide a more perfect glass to metal seal than has heretofore been found possible.

Another object is to provide a laminated-alloy metal sealing member, and a novel method of producing the same.

Another and more specific object is to provide for production of such a metal sealing member according to the technique of powder metallurgy.

Other objects and advantages of the invention will hereinafter appear.

Heretofore in the use of alloys rich in cobalt for sealing with glass considerable difiiculty has been encountered in obtaining a uniform oxide coating of maximum mechanical strength when the glass to metal seal is finished and gas-tight or vacuum-tight. Thus with a metal sealing member composed of an alloy of 29 per cent nickel, 17 per cent cobalt, 0.3 per cent manganese, and balance iron (which alloy is sold commercially under the trade-name of Kvar) it was found that such a member when heavily oxidized so as to afiord a mechanically strong seal with a suitable high melting point glass was likely to be porous in the oxidized area, with a resultant lack of vacuum-tightness; whereas such a metal member when lightly oxidized so as to insure a vacuum-tight seal with such glass, resulted in a seal which was inherently relatively weak mechanically.

On the other hand, an alloy containing 42 per cent nickel, 6 per cent chromium, and 52 per cent iron (which alloy is sold commercially under the trade-name of Sealmet No. 4) contains enough chromium so that the chromic oxide layer formed by processing the alloy in a hydrogen furnace, with the hydrogen saturated with Water vapor at about 90 degrees F'., gives, under these conditions, a protective layer of chromic oxide sufficiently thick and of proper nature to prevent subsequent formation of iron oxide. Moreover, this chromic oxide layer partially dissolves in the molten or fused glass and furnishes a substantially perfect vacuum tight seal of unusual mechanical strength. Stated another way, the chromic oxide layer formed on the last mentioned alloy, by heat treatment at a high temperature in wet hydrogen, is sufiiciently adherent and impermeable on the exposed surface of the alloy itself to prevent oxidation of iron in the alloy underneath, even in the highly oxidizing flames on the high speed production equipment of present manufacturing processes; and at the same time such oxide layer is adapted to flux with the glass to afford a vacuum-tight and unusually strong mechanical bond.

Although the alloy just described is better suited for sealing to the glass and gives a mechanically stronger bond than that of the first mentioned alloy, such Sealmet No. 4 alloy does not match so well the non-linear thermal expansion characteristics of high melting point glasses having low coeflicients of thermal expansion as does the aforementioned iron, nickel, cobalt alloy, rich in cobalt.

In accordance with my invention the best properties or characteristics of both of the aforementioned alloys are obtainable in a single metal member forming an essential part of the glass to metal seal, by applying the principles of powder metallurgy, as will now be described. Thus, a molding cavity of any suitable or preferred size is eighty per cent filled with thoroughly mixed metal powders as follows, having substantially the following proportions, by weight: nickel 29 per cent; cobalt 17 per cent; iron 53.7 per cent, and manganese 0.3 per cent. The upper surface of said eighty per cent fill is leveled in any well known manner, and the remaining twenty per cent of the molding cavity is filled with the following metal powders likewise thoroughly mixed in substantially the following proportions, by weight: nickel 42 per cent, chromium. 6 per cent, and iron 52 per cent.

The mixtures of powdered metals within said molding cavity are then jointly or simultaneously subjected to a suitable molding pressure (say, 10,000 to 20,000 pounds per square inch) to provide a prepressed slug or unit of about 0.3 inch thickness which is adapted to withstand the ordinary handling involved in the next step of treatment thereof. Such prepressed slug is then subjected to a suitable heat sintering operation at about 2200 to 2300 degrees F. in an atmosphere of dry hydrogen, dried over molten sodium. The sintered slug is then subjected to a rolling operation, to effect a reduction of approximately fifty per cent in the thickness thereof, with a proportional increase in the upper and lower sur- With the slug thus reduced to approximately one.-

eighth of its original thickness, and of approximately eight times its original upper andlower surface areas, it is heat treatment, after which it is rolled, without further heat treatment, .to a thickness of apis then inch. The rolled plate hydrogen, then punched or cut proximately .010 annealed in dry into blanks of suitable form, andeach blank then drawn into the form of a cup, as shown and described in that form of my invention applied to a glass tube or envelope, or each blank when of suitable shape may be drawn. into the form of an annulus of channel form in transverse cross sec tion, as shown anddescribed in that form of my invention applied to a metaltube or envelope, whereinone or more of the members of cup form will also be employed.

With a plate thicknessof approximately .010 inch, as aforedescribed, it is to be understood that the layer of the Kovar? alloy will be about .008 inch thick, and the layer of Sealmet No. i alloy will be about .002 inch thick. 7 The blank will usually be drawn in a for. exterior location of the Sealmet No. 4 alloy when a cup-shaped member is required, and the blank will be drawn to provide'for interior location of the Sealmet No. 4 alloy when a member of annular form is required.

The accompanying drawings illustrate certain embodiments of my invention which will now bedescribed; it being understood that the embodiments illustrated are susceptibleof modification in respect of certain structural details thereof and/or in respect of the specified percentages of the ingredients of the respective alloys .without departing from the spirit and scope of -my invention as defined in the appended claims.

In the drawings, Figure 1 is a side elevational view illustrating somewhat diagrammatically a prepressed or molded slug or unit having sired proportionality of thicknesses of the respective layers of the two groups of powdered alloy ingredients.

Fig. 2 is a similar view of the slug or unit of Fig. 1 after heat sintering thereof in an atmosphere of dry hydrogen thereof for eifecting a reduction of approximately fifty per cent in its thickness, and a corresponding increase in the upper and lower surface areas thereof.

Fig. 3 is a similar view of the rolled slug of Fig; 2 after heat treatment of the latter and rolling thereof to effect a reduction of approxh.

mately fifty per cent in its thickness.

Fig. 4 is a similar view-f the rolled slug (or laminated plate) of Fig. 3 after a'suitable heat treatment of the latter sand rolling thereof to effect a further reduction in thickness of about fifty per cent.

Fig. 5 is an elevational view of a laminated cupiproduced in accordance with my invention; a fragment of the cup being. cut. or broken away, and the wall section magnified to show the. relatively thin and relatively thick layers of the. respective alloys.

then subjected to anothermanner to provide the deand subsequent rolling Fig. 6 is a fragmentary view, partly in section and partly in elevation, of a glass tube or envelope having one of my improved laminated alloy sealing members sealed thereto and supported thereby.

Fig. '7 is a fragmentary view, partly in section and partly in elevation, of a metal tube or envelope having a laminated alloy member of annular form the exterior alloy layer of which is peripherally united with the inner surface of the metal tube, a body of glass being sealed to the inner alloy layer and to the outer alloy layer of a cup-shaped member of the character shown in Figs. .5 and 6, and

Fig. 8 is. a fragmentary elevational view of one of the conducting metal terminal or supporting members prior to rigid and permanent attachment thereof to the cup member by welding.

Referring to Fig. 1, the numeral i0 designates a molded slug or preform preferably composed ofa relatively thick layer I0 consisting of a thorough mixture of 29 per cent nickel, 17 per cent cobalt, 53.7 per cent iron, and 0.3 per cent manganese; whereas the relatively thin layer I0 consists of .a thorough mixture of 42 per cent nickel; 6 percent chromium, and 52 per cent iron; all of said metal ingredients being initially in powder form, and the slug as a whole having been molded at a suitable pressure, of from 10,000 to 20,000 pounds per square inch, to integrally unite said layers with each other, and to provide for handling or" the slug without chipping thereof or disintegration of the ingredients of the respective layer. cally that. thelayer I0 comprises approximately one-fifth of the total thickness of the slug and the layer 10* comprises the remainder of such thickness.

The slug ID, of about 0.3 inch thickness, is then sintered, in an atmosphere of dry hydrogen, at a temperature of about 2200 to 2300 degrees F., to effect at least partial alloying of the particles of the ingredients of the respective layers. Slug I0 is then rolled to reduce the thickness thereof by about. one-half, as shown at it in .Fig. 2. The rolled slug w of Fig. 2 is then subjected to a second'heat treatment, at a sufficiently high temperature to anneal the same; that is, to counteract the effect upon the ingredients of the respective layers of the aforementioned rolling operation. The slug of Fig. 2 is then rolled to reduce its thickness by about one-half, as shown at 10* in Fig. 3; and the twice rolled slug or plate of Fig. 3 is then subjected to a heat treatment like that last mentioned. The heat treated plate of Fig. 3 is then subjected to a rolling operation to reduce its thickness by about one-half, to providethe plate shown at H3 in 4. Thereupon the plate I0 of Fig. 4 is subjected to a heat treatment like that last mentioned; whereupon the plate 10 without further heat treatment, is rolled a sufficient number of times to reduce the thickness thereof to approximately ten-thousandths of an inch. After completion of the last mentioned rolling operation, the plate (not shown) is annealed at a suitable temperature in an at mosphere of dry hydrogen. Said completely rolled and annealed plate is then subjected to a cutting or punching operation to provide a multiplicity of sheet metal blanks of the desired size and contour.

In practice the metal blanks (not shown) are punched in circular form when a cup-shaped memberilike that. shown at le (in Figs. 5, 6 and?!) is to be produced; or

The line it shows diagrammatiblanks of annular.

form, and of substantially greater diameter, are punched from the metal plate, when annular members like that shown at w in Fig. 7 are to be produced. Said circular blanks are subjected to any suitable or well known type of drawing or forming operation to provide cup-shaped members like that shown at it. After drawing or forming of such blanks the peripheral wall surrounding the open end of each member lt may be cut or ground to provide a straight edge portion 58 to provide a more finished appearance to the article.

As shown in Fig. the relatively thin layer tu of the ferrous alloy rich in chromium is located upon the exterior of member HF, and the relatively thick layer iil is located interiorly of member Hi The cup-shaped members lt in the final form thereof shown in Fig. 5, are then subjected to a suitable moist hydrogen, whereby there is produced upon the outer or exposed surface areas of the same a protective layer of chromic oxide (not shown) which is suificiently adherent and impermeable to insure against oxidation of iron in the alloy layer Hi Prior to sealing the metal member te into a tube H of high melting point glass (such as Corning No. 705-2 glass, for example, which is a well known type of borosilicate glass) member Hi has rigidly attached thereto suitable lengths l2 and iii of a solid metal rod, preferably composed of ni kel or iron, as by Welding the adjacent ends of members 52 and E3 to the inner and outer surfaces respectively of the closed end wall it? of member Hi Said adjacent ends of members 62 and i3 are preferably initially of convex form, as shown at 52* in Fig. 8, to facilitate uniting of members l2 and it to wall 5& by a sort of spotwelding operation; the welding current being passed between members l2 and it through said wall m The portion 5& of wall H3 is preferably not completely fused as an incident to the welding operation; but as a precaution I prefer to apply an annular filler of silver solder, or the like, between the inner surface of wall I8 and the periphery of member l2, to insure a sealing connection between these metal parts, and to strengthen the mechanical connection between wall HF and member 52; which latter is adapted to serve as one of the circuit terminals of the tube; say, the anode terminal. The member 13 has attached thereto any suitable form of anode (not shown) which is supported thereby.

With the parts properly positioned (Fig. 6) the portion ii of the glass tube ii is fused in any well known manner; a portion of the chromium oxide layer upon the outer surface of member lt being dissolved in the contacting part of the portion H of tube it when said portion is in fused condition. By this means a vacuum-tight and mechanically strong seal or connection is provided between the member Hi and portion i l of the vacuum tube M.

It is to be particularly noted that in the use of the aforementioned alloys in laminated form the portion H of the tube ii is not sealed to the ferrous alloy high in cobalt Fig. 5). Further, it is to be understood that a strain-free seal between the glass tube ii and the member Hi is not produced. However, adequate freedom from strain is obtained. The layer 10- of alloy (composed of iron, nickel and chromium) is under strain; but such alloy is of a ductile nature so that it is able to follow the iron, nickel, cobalt alloy base portion lil to which it is integrally united or bonded; which portion Ill has substanheat treatment in wet or tially the same coefiicient of thermal expansion, and substantially the same non-linear variation of said coeincient of thermal expansion as the aforementioned high melting point glass of tube ii to which the cup-shaped member Hi is sealed.

In the metal type vacuum tube shown in Fig. 7 the numeral i i designates the main hollow metal body portion, into the open upper end of which the aforementioned annular metal sealing member te is telescoped, with the open end of the channel of member @93 facing upwardly, and with the upper edges w and M of said members in substantial alinement. Member W may be produced from a blank punched from the laminated alloy plate aforementioned; but in this instance the blank is drawn in such a manner that the relatively thick layer of ferrous alloy rich in cobalt is located exteriorly of member 16, as indicated by numeral 5:3 whereas the relatively thin layer of ferrous alloy rich in chromium is iocately interiorly of member E8 Member Hi and member Hi are mechanically united by any desired number of spot-welds around the periphery of these parts; and thereafter a continu" one line of welding or brazing material is applied to the aforementioned upper edges iii and W, to rigidly and permanently unite the latter and form a vacuum-tight seal therebetween, as inicated at 55.

A laminated alloy sealing member Hi aforedescribed, is likewise employed in the vacuumg t seal of Fig. 7; member 1& having an iron or nickel terminal rod it positioned upon and attached to the outer surface of the closed end wall HF, and an iron or nickel anode supporting rod i i positioned upon and attached to the inner surface of said closed end wall Hi by a welding operation of the character aforedescribed. A fillet of silver solder or the like (not shown) may be applied between the periphery of either the end of rod H5 or the end of rod ii and the respectively adjacent surface of said end wall H1 A tubular glass member it composed of the aforementioned high melting point borosilicate glass is positioned in telescopic relationship to the outer surface of the i verted cup-shaped member lt and to the inner surface it of the inner circular wall of the upwardly opening annular member it so that upon fusing of the overlapping end portions Ed and 48* the same will be united in a mechanically strong and vacuum-tight relationship to the members MW and it the thin layers lii lil of. said members being composed of the aforementioned alloy rich in chromium; the layers of chromium oxide on the respective members assisting, as aforedescribed, in providing for attainment of the desirable results herein contemplated.

Although I have hereinabove indicated a preference for a proportionality of ingredients corresponding with that of the Sealmet No. 4 ferrous alloy rich in chromium; it is to be understood that other ierrous alloys rich in chromium may be empioyed. For example, I may provide a relatively thin layer for scaling to the borosilicate glass in which seventy per cent of the mixture of metal powders consists of iron the remaining thirty per cent of which mixture consists of chromium; the relatively thick layer of ferrous alloy rich in cobalt preferably having a proportionality of its ingredients corresponding with that of the aforementioned iiovar alloy.

I claim:

1. A metal member adapted for sealing to a body of high melting point glass, said member comprising eanablayerecl integrally molded ferrcus alloy, one of said layers comprising approximately 29 per cent nickel, 17 per cent cobalt, 0.3 per cent manganese, remainder iron, thereby affording a cceificient of expansion for said layer which approximates that or said glass body, 211G the other or" said layers being relatively thinner and comprising approximately 42 per cent nickel, 9 per cent chromium, remainder iron, to afford fusion thereof with said. g ass body to effect a strong inecliai eel seal therebetween.

2. The method of king eicc in which a body of high melting point glass is sealed. to a metallic member, which comprises forming the member a of alloy having a thermal expansion characteristic matching that of said glass integrally united with an overlying layer of rich in a metal Whose ride is soluble in glass, oiiicliting the exposed surface of the iatcer layer and then sealing the glass to said. outer layer.

3. e metl'iod of ma ring an electrical device in which y of hi, 1 melting point glass is sealed. to a etailic n.- inber, which comprises the'steps of forming the member of a layer of alloy rich in cobalt and a thermal exnansion characteristic matching that of said glass integrally unit with an overlying layer of alloy rich in chromium, oxidizing the exposed surface of the latter layer, and then fusing the glass to said oxidized alloy snri'ace.

4. A glass metal seal member fusion 8;? characteristic and expansion coeflicient compatible with high melting point glass, comprising integrally united layers of an alloy comprising approximately 29 per cent nickel, 17 per cent cobalt, 0.3 per cent manganese, remainder iron, and analloy comprising approximately 42 per ccnt'nickel, 6 per cent chromium, remainder iron.

References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 1,348,182 Koebel. Mar. 8, 1932 1,993,023 Scott Mar. 5, 1935 2,962,335 Scott Dec. 1, 1936 2,219,423 Kurtz Oct. 29, 1940 2,219,573 Fraenckel Oct. 29, 1940 2,241,095 Marvin May 6, 1941 2,267,954 Schumacher Dec. 30, 1941 2,274,999 Allen Mar. 3, 1942 2,288,184 Dodson June 30, 1942 2,332,416 Waltenberg Oct. 19, 1943 2,323,162 Talmage June 29, 1943 2,343,938 Allen et a1 Feb. 29, 1944 2,350,491 Butler et a1. H June 6, 1944 2,369,146 Kingston Feb. 13, 1945 2,394,919 Kingston Feb. 12, 1946 2,398,529 Holmquist Apr. 16, 1943 2,399,758 Pierri May 7, 1946 2,422,628 McCarthy June 17, 1947 2,442,223 Uhlig May 25, 1948 2,446,277 Gordon Aug. 3, 1948 2,502,855 Kingston Apr. 4., 1950 2,515,337 Clark July 18, 1950 

1. A METAL MEMBER ADAPTED FOR SEALING TO A BODY OF HIGH MELTING POINT GLASS, SAID MEMBER COMPRISING A DUAL-LAYERED INTEGRALLY MOLDED FERROUS ALLOY, ONE OF SAID LAYERS COMPRISING APPROXIMATELY 29 PER CENT NICKEL, 17 PER CENT COBALT, 0.3 PER CENT MANGANESE, REMAINDER IRON, THEREBY AFFORDING A COEFFICIENT OF EXPANSION FOR SAID LAYER WHICH APPROXIMATES THAT OF SAID GLASS BDOY, AND THE OTHER OF SAID LAYERS BEING RELATIVELY THINNER AND COMPRISING APPROXIMATELY 42 PER CENT NICKEL, 6 PER CENT CHROMIUM, REMAINDER IRON, TO AFFORD FUSION THEREOF WITH SAID GLASS BODY TO EFFECT A STRONG MECHANICAL SEAL THEREBETWEEN. 